A comparison of three studies of the influence of expert testimony on jurors

Three conceptual replications of the effects of expert testimony on jurors' decisions and behaviors were compared. Taken together, these studies demonstrated significant increases in jurors' scrutiny of the evidence presented to them and significant reductions in their beliefs in the general accuracy of eyewitness testimony. The overall effect of expert testimony had a combined probability ofp=.0000084. This means that these combined results would occur by sampling bias alone less than one time out of 100,000. Expert testimony accounted for 3% of the variance in verdicts and 68% of the variance in the time jurors deliberated about eyewitness testimony. Several implications of these findings for psychologists investigating eyewitness identification and for the criminal justice system are discussed.I would like to thank James V. Devine, Judith P. Goggin, Elizabeth F. Loftus, and Gary L. Wells for their valuable comments on an earlier draft of this article.     

Two conjectures about the issue of expert testimony

This article responds to concerns about expert testimony in experimental psychology by conjectur that disagreements about the propriety of the testimony are camouflaged arguments about the strength of psychological knowledge. Differences between proponents and opponents of expert testimony are about the state of psychological knowledge and certainty, rather than about the proper standard for psychologists to use when deciding whether to testify. A second conjecture is stimulated by the assumption that laypersons generally overvalue eyewitness testimony and that expert psychological testimony is a required corrective. The truth of this assumption rests on the debatable assertions that eyewitness identifications, without more, are potent sole determinants of trial outcome, and that lay juries need instruction from experimental psychologists about aspects of human behavior of which the jurors are definitive producers and consumers. One need not resolve these debates in order to understand that psychologists should not rely on the legal community to set the psychologists' standards for expert testimony. And psychologists, in considering their role as courtroom experts, should guard against a self-serving critique of the acumen of lay juries.     

Impact of Defense-Only and Opposing Eyewitness Experts on Juror Judgments

Previous research shows that expert testimony on eyewitness memory influences mock-juror judgments. We examined the extent to which opposing expert testimony mitigates the impact of defense-only expert testimony. Participants (N = 497) viewed a video-taped trial involving an eyewitness identification and individually rendered verdicts and evaluated the evidence and the experts. We manipulated the Foils (unbiased vs. biased) and Instructions (unbiased vs. biased) of the lineup and Expert Testimony (no expert vs. defense-only expert vs. opposing experts). Expert testimony did not significantly influence juror judgments, but the opposing expert testimony diminished the credibility of the defense expert in the eyes of the jurors. Results point to the need for further research on conditions that qualify the impact of expert testimony.     

Courtroom testimony by psychologists on eyewitness identification issues

This article makes two major points in regard to expert psychological testimony on eyewitness identification. First, the attention devoted by psychologists to eyewitness identification issues is far out of proportion to the incidence of trials involving eyewitness identifications of criminal defendants; furthermore, the often-expressed concern over wrongful convictions is probably misplaced. Second, the experimental methods used in studies of eyewitness performance are fundamentally unsuited for drawing conclusions about actual witnesses. Hence, there is not an adequate scientific foundation for expert psychological testimony on eyewitness identification. Archival research is perhaps the most promising approach to the study of the criminal justice system.     

The impact of general versus specific expert testimonyand eyewitness confidence upon mock juror judgment

Subjects (n=128) initially viewed an eyewitness of high or low confidence. Subsequently, participants viewed a psychologist who gave either espert testimony on the unreliability of eyewitness identification, specific expert testimony, or no expert (control) testimony. Subjects viewing expert testimony believed the eyewitness identified the gunman significantly less often, gave the defendant lower guilt ratings, estimated a lower general percentage of correct identifications under similar circumstances, estimated a lower percentage of general accurate eyewitness testimony, and gave significantly lower ratings to the belief that one can generally tell from eyewitness confidence whether an eyewitness is accurate than subjects in control conditions. Significant differences were also obtained between general and specific expert testimony. Participants viewing specific expert testimony estimated lower general percentages of correct identifications under the circumstances of the crime and reported relying more upon the psychologist's testimony than subjects viewing general expert testimony. Additionally, subjects viewing general expert testimony had significantly less confidence in their gunman vs. innocent person decision than subjects in specific testimony or control conditions. Subjects who viewed the high confidence eyewitness decided that the eyewitness correctly identified the gunman more often, gave the defendant higher guilt ratings, and estimated the general percentage of accurate eyewitness testimony to be significantly higher than jurors in low eyewitness confidence groups. The finding that jurors may continue to rely on eyewitness confidence to gauge the accuracy of the witness even after viewing expert testimony is discussed.     

Legal principles governing expert testimony by experimental psychologists

With increasing frequency, experimental psychologists are called upon to present their research findings and theories in a courtroom. This article reviews the general evidentiary standards regarding such expert testimony, with a specific emphasis on how those principles have been applied in the context of expert psychological testimony on the unreliability of eyewitness identifications. A comprehensive review of the judicial decisions in this area reveals that there has recently been a significant shift in the courts' receptivity toward such testimony. Many courts now believe that psychological research on human perception and memory has progressed to the point that the expert's testimony may be considered both reliable enough and helpful enough to the jury to justify its adminssion in the appropriate case. The author concludes with a discussion of several developments that would help to allay the judicial system's historical concerns over the admission of such expert psychological testimony.     

Can experts help jurors to evaluate eyewitness evidence? A review of eyewitness expert effects

Courts occasionally permit psychologists to present expert evidence in an attempt to help jurors evaluate eyewitness identification evidence. This paper reviews research assessing the impact of this expert evidence, which we argue should aim to increase jurors' ability to discriminate accurate from inaccurate identifications. With this in mind we identify three different research designs, two indirectly measuring the expert's impact on juror discrimination accuracy and one which directly assesses its effect on this measure. Across a total of 24 experiments, three have used the superior direct methodology, only one of which provides evidence that expert testimony can improve jurors' ability to discriminate between accurate and inaccurate eyewitness identifications.     

Ten years in the life of an expert witness

American Courts are experiencing increased use of expert testimony based upon psychological research. Ten years ago, I began testifying about my own research on human perception, recollection, and eyewitness accounts. The growing acceptance of this testimony percipitated a backlash from some psychologists. This essay describes the chronology of these events, and their relevance for the more general use of psychological research as evidence in court.     

The Impact of Eyewitness Expert Evidence and Judicial Instruction on Juror Ability to Evaluate Eyewitness Testimony

It has been argued that psychologists should provide expert evidence to help jurors discriminate between accurate and inaccurate eyewitness identifications. In this article we compare the effects of judicial instruction with expert evidence that is either congruent or incongruent with the ground truth, focusing on juror ability to evaluate “real” eyewitness evidence. In contrast to studies which have employed “fictional” eyewitness designs, we found no appreciable effect of either congruent or incongruent expert evidence on participant-juror sensitivity to eyewitness accuracy. We discuss the role of methodology on the inferences and conclusions that can be made regarding the impact of eyewitness expert evidence.     

Expert Testimony Regarding Child Witnesses: Does It Sensitize Jurors to Forensic Interview Quality?

Does expert testimony on forensic interviews with children help adults distinguish between poorly conducted and well-conducted interviews? This study evaluates the effects of social framework expert testimony regarding child witnesses in a case involving allegations of child sexual abuse. A 2 (Expert Testimony: present or absent) × 3 (Child Forensic Interview Quality: poor, typical, or good) × 2 (Child’s Age: 4- or 10-year-old) factorial design was used to examine whether expert testimony is prejudicial or beneficial to jurors (N = 463). The results revealed that, without expert testimony, mock jurors did not consider the forensic interview quality when reaching a verdict. However, with expert testimony, mock jurors were more likely to render guilty verdicts if the interview quality was good versus poor. Further expert testimony increased mock jurors’ knowledge about child witnesses. These findings suggest that expert testimony related to the impact of interview techniques on the reliability of children’s reports may assist fact-finders in evaluating child abuse cases.     

Effects of Experiencing the Eyewitness Identification Procedure on Juror Decisions

Mistaken eyewitness identifications are believed to contribute to a preponderance of wrongful convictions, underscoring the need to identify methods to help decrease the likelihood of false convictions based on eyewitness testimony. The present study tested the hypothesis that providing jurors with first-hand experience with eyewitness identification procedures could help further sensitize them to the limitations of eyewitness testimony. Eighty college students watched a videotaped mock trial in which the prosecution’s sole evidence was eyewitness testimony. In a 2 × 2 randomized factorial design, we manipulated whether participants heard expert psychological testimony (henceforth referred to as expert testimony) on the limitations of eyewitness identification and whether they experienced an eyewitness identification procedure. As predicted, experiencing the eyewitness identification procedure had a significant impact on juror decisions, suggesting that this procedure could further help reduce the likelihood of wrongful convictions.     

The importance of forensic evidence for decisions on criminal guilt

Recent studies have found that the general public perceives forensic evidence to be relatively inaccurate and to involve high levels of human judgement. This study examines how important the general public finds forensic evidence by comparing decisions on guilt and punishment in criminal cases that involve forensic versus eyewitness testimony evidence and examining whether a CSI effect exists. Specifically, this experimental survey study utilized a 2 (crime type: murder or rape) × 4 (evidence type: DNA, fingerprint, victim eyewitness testimony, or bystander eyewitness testimony) ? 1 (no victim testimony for murder scenario) design, yielding seven vignettes scenarios to which participants were randomly assigned. Results indicate that forensic evidence was associated with more guilty verdicts and higher confidence in a guilty verdict. Forensic evidence did not change the expected sentence length and did not generally affect the ideal sentence length. However, for rape, respondents believed that the defendant should receive a longer sentence when forensic evidence was presented but forensic evidence did not alter likely sentence that respondents expected the defendant to receive. The results of this study did not support a CSI effect. Overall, this study suggests that forensic evidence – particularly DNA – has a stronger influence during the verdict stage than the sentencing stage.     

Comparing the effectiveness of <Emphasis Type="Italic">Henderson</Emphasis> instructions and expert testimony: Which safeguard improves jurors’ evaluations of eyewitness evidence?

Objectives

The New Jersey Supreme Court recently determined that jurors may not be able to effectively evaluate eyewitness evidence on their own. As a result, the Court proposed the use of judicial instructions to assist jurors (called Henderson instructions) and suggested the implementation of these instructions would reduce the need for expert testimony. We tested the efficacy of these instructions compared to alternative instructions and expert testimony.

Methods

We utilized a mock trial paradigm, randomly assigning 452 participants to 1 of 20 videotaped trial conditions that varied the quality of eyewitness evidence (both witnessing and identification conditions) and the type of safeguard presented during the mock trial.

Results

Jurors were sensitive to the quality of identification conditions on their own. Jurors were more likely to convict when identification conditions were good and less likely when identification conditions were poor. This relationship was mediated by eyewitness credibility ratings. Expert testimony resulted in skepticism by reducing the likelihood that jurors would convict regardless of the quality of witnessing and identification conditions. No variation of the instructions influenced verdicts.

Conclusions

While jurors were sensitive to the quality of identification conditions on their own, we observed no such effect for the quality of witnessing conditions, even with the aid of instructions and/or expert testimony. Both Henderson instructions and expert testimony may be insufficient for assisting jurors to effectively evaluate problematic witnessing conditions. Future research should examine the use of alternative safeguards.

     

Influence of expert testimony regarding eyewitness accuracy on jury decisions

To determine the influence of expert testimony regarding the general unreliability of eyewitnesses, a two-phase study was conducted. In the first phase, 24 community residents served as jurors on four six-person juries. A burglary case was tried in 120 District Court. El Paso, Texas. Two juries heard all the evidence including the expert testimony of a psychologist and the other two heard all of the testimony except that of the psychologist. During the second phase, 24 student jurors constituting four six-person juries viewed a videotape of the trial. Two of these juries saw the entire proceeding from the first phase including the expert testimony and the remaining two saw all but the expert testimony. All juries acquitted the defendant; however, those who heard the expert testimony significantly lowered their judgments of the accuracy and reliability of eyewitness identification as well as its overall importance to the trial. Further, those juries that heard the expert testimony spent a significantly longer time discussing eyewitness identification as well as other relevant evidence. No differences between community residents and college student juries were obtained.The authors wish to thank Judge Brunson Moore, Mr. David Jeans, Mr. Ricky Glenn Smith, Detective James Christianson, D. Steven Cooper, Rachel Hanna, Daniel Torres, and Patricia Tetreault. All of these people participated in the trial and without them this research could not have been conducted. This research was supported by Gift Funds of the Department of Psychology, University of Texas at El Paso.     

Juror Sensitivity to the Cross-Race Effect

Black and White mock jurors' sensitivity to the cross-race effect was investigated by varying the race of the eyewitness in a simulated murder trial of a Black defendant. Participants heard an audiotape of a trial after which they rendered a verdict and rated the credibility of the witnesses. White participants found the prosecution witnesses (including the eyewitness) more credible, and the defense witness less credible, than did Black participants; they were also more likely to find the defendant guilty. The Black eyewitness was perceived as more credible than was the White eyewitness, but eyewitness race had no effect on verdict. These results are consistent with the literature indicating that jurors of different races reach different verdicts, and also that jurors are relatively insensitive to factors that affect eyewitness testimony, such as the cross-race effect.